firstboot: fix segfault when --locale-messages= is passed without --l…

…ocale=

\#0  __strcmp_evex () at ../sysdeps/x86_64/multiarch/strcmp-evex.S:295
No locals.
\#1  0x0000557444eb172b in process_locale () at ../src/firstboot/firstboot.c:342
        etc_localeconf = 0x7ffd40217b80 "/root/root/etc/locale.conf"
        locales = {0x0, 0x0, 0x0}
        i = 0
        r = <optimized out>
        __PRETTY_FUNCTION__ = "process_locale"
        __func__ = "process_locale"
\#2  0x0000557444eaff93 in run (argv=0x7ffd40217d98, argc=3) at ../src/firstboot/firstboot.c:1401
        loop_device = 0x0
        unlink_dir = 0x0
        r = <optimized out>
        loop_device = <optimized out>
        unlink_dir = <optimized out>
        r = <optimized out>
        __func__ = <optimized out>
        __PRETTY_FUNCTION__ = <optimized out>
        enabled = <optimized out>
        _error = <optimized out>
        _level = <optimized out>
        _e = <optimized out>
        _level = <optimized out>
        _e = <optimized out>
\#3  main (argc=3, argv=0x7ffd40217d98) at ../src/firstboot/firstboot.c:1432
        r = <optimized out>
        __PRETTY_FUNCTION__ = "main"

Fixes systemd#25249

(cherry picked from commit 4c4a73c)
(cherry picked from commit a693cba)

src/firstboot/firstboot.c

@@ -334,7 +334,7 @@ static int process_locale(void) {
 
         if (!isempty(arg_locale))
                 locales[i++] = strjoina("LANG=", arg_locale);
-        if (!isempty(arg_locale_messages) && !streq(arg_locale_messages, arg_locale))
+        if (!isempty(arg_locale_messages) && !streq_ptr(arg_locale_messages, arg_locale))
                 locales[i++] = strjoina("LC_MESSAGES=", arg_locale_messages);
 
         if (i == 0)